Glass



mama Mar. 10, 1925.

UNITED STATES.

ATENT OFFICE.

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80 Drawing.

sulator at high temperatures. Another object of .the invention is to provide a glass made from a large amount of calcium fluoride and having the quality of transparency and having also substantially no alkali content. A further object of the inventionis to provide a glass with substantially no alkali content and a high'alumina content. Still another object of the invention is to provide a glass having a low silica content,

a high alumina content, substantially no alkali content, low expansion and high elec- Lead trical insulation under heat. Another and still further object of the invention is to provide a transparent fluoride glass with substantially no alkali content. A still further object of the invention is to provide a glass with substantially no alkali content and having the charactertistics of low expansion and high electrical insulation under heat. Other and further objects of the invention will be hereinafter pointed out and 1 will beset forth in the appended claims.-

The glasses forming the subject matter of this invention may be considered from two different viewpoints: First, a glass adapted for electrical insulators, including spark plugs, and capable of withstanding an electrical current at high temperatures; and, second, a glass adapted for optical purposes and having the properties of transparency while being made from a. batch which has a high calcium fluoride content. From the first viewpoint, we have found in glasses that electrical insulation under heat is directly proportional to the alkali content of the glass, that is, the higher the alkali content, the poorer the electrical insulation under heat, and that this insulation decreases as the heat is increased. For instance, an insulator one inch thick made of glass containing about 4.5% of alkali (considered a low content) will withstand an Applhaflon'fled December-8, 1m. Sci-1:110. mm.

electrical current exceeding 180,000 volts at atemperature'at about 70 F. but, when this same insulator is heatedto 800 F., itsv dielectric s'tren h is reduced to zero and it becomes a con uctor.

From a second viewpoint, we have discovered that fluoride compounds, such as calcium fluoride (fluorspar) may be usedin very large amount, say up to 35% of a batch to produce a transparent glass which will not aflect the melting pot as other fluoride glasses usually do, this being believed to be due to the fact that a larger amount of alumina is used, in the batch.

. The following tables area number of'raw batches made m accordance with this invention:

Silica."- 30 37 40 34.5 35 25 43 50 Alumina, hydrated '18 16 15 25 30 Boric acid 25 17 14 28 15 20 luorapgr 10 10 8.5 7 7 25 12 20 -Magnes1um carbonat 3 oxid 16. 5 28. 5 15 In the following table the glasses a to h, inclusive, are glasses calculated from the batches 1 to, 8, inclusive, of the foregoing table, whereas the glass 13 is additional glass made in accordance withthis invention:

'abcdeffl All of the above glasses have a low silica content, that is a content not exceeding 70%, and we are aware that this contentmay be reduced as low as 25% and stillv obtain some of the results of thisinvention.

' It will be noted that-all the batches as well as the glasses contain large amounts .of alumina. In the examples given, the finished glasses contain .from 12.6% to 32.5% of alumina, but it. will be understood that the invention is not confined to these limits, as it has been found that someof the results of this invention may be secured by providing an alumina content of 10% to 35% in the finished glass. Alumina has not heretofore been used in low-expans on glasses in large amounts because when commed with an alkali, it will produce large expansion or make the glass so hard that it is impracticable to work. In this invenglazes for the purpose of producing opalescence in the lasses or glazes, and, when so used, has had the effect ofeating'away the ots or vessels used in melting the batch. n this invention, large amounts of fluospar (from 5% to 25% of the batch) are used and clear glasses are produced without affecting the melting pot, t

is bein believed to be due to the large amount of a umina which neutralizes the effect of the fluorspar (calcium fluoride) on the melting pot and takes away the property of producing opalescence. This appears to be shown from the fact that, in'the above glasses, the lowering of the alumina content will make the glasses opalescentand will increase the action on the melting pot, and increase the expansion of'the glass when calcium fluoride is used,

' the finished glass will show from analysis calcium oxide and the the same time, decreasing the liability to- In some of the-batches orming part of this invention, the boric oxid has been partially .be used, in some cases.

replaced by lead for the increasing of fusibi ity and workability of the batch, while, at

crystallization and has a tendency to better its insulation. Instead of lead,barium may The linear co-efiicient of expansion of most of the glasses is less than .0000050.

A further advantage of. glasses made in accordance with this inventlon is high sta bility against the attack of steam, water, acids, and atmospheric conditions and fair stability against alkalies, this latter being unusual as glasses heretofore made with substantially no alkali content are readily attacked by alkali solutions, especially under the action of heat. Glasses made in accord-- ance with this invention may be melted or worked in the ordinary pot or tank and may be soft and plastic through a considerable range of temperature allowing them to be pressed or blown into shape in the ordina manner. Furthermore, a transparent optical glass may be obtained from a batch high in fluorine. I

presence ,of fluorine.

This invention provides a glass which is free from alkali or has such, a small alkali content as not to interfere with electrical resistance under heat. In addition, a glass I is provided which is clear and transparent, has low expansion, good stability and electrical resistance under heat up to the softening point of the glass, this softening point being variable according to the. composition of the glass from 500 centigrade to 900 centigrade. These characteristics are particularly desirable in the spark plug insulator which is exposed to high heat, large temperature changes and hard mechanical stresses, so that a glass of a low co-eificient of expansion, good mechanical strength, and a igli softening point, as well as a high electrical insulation under heat .is required.

Heretofore glasses have been made which have had one or more of the desirable properties hereinbefore mentioned, but so far as we are aware no glass has been produced whichhas the following characteristics: low expansion, good stability to mechanical attacks or the attacks of the atmosphere or other elements, capable of being melted and worked in theordinary furnaces used in glass making without crystallization in the ots or hardness to workability, high insuation under heat, and a high softening oint. Some of the glasses set forth are opal in color, while others are clear transparent glasses and it is to be understood that the in vention is not limited as to its color.

In the specification and claims, the glass is described as having-high electrical insulation under heat and by this is to be understood a glass which will have an efiective temperature (to) resistivity of at least 500 .oentigrade, as measured by the Bureau of Standards in Aeronautic Power plants report 18, Washington, D.- 0., January 6th, X

It will be understoodthat this invention is 7 not limited to the compositions or percentages hereinbefore set forth as we are aware that many changes may be made in the compositions and thepercentages and other ele-v ments added, but we have further found that within the hereinbefore mentioned limits the best glasses seem to be produced.

' The new glassherein described is particularly adapted'for use as insulators for spark plugs. Its transparency enables the user to ascertain at oncethe condition of all of the spark'plugs and note if all are firing progerly as the flash of each explosion can distinctly seen through the spark plug if thespark plug is working ro erly. It may also be ascertained throug' t e spark plug if the gasoline mixture is of correct lpro ortion for if the mixture is too rich t e ture is right the flash is of alight blue color. Bythe used the term, glass, in the speciash is of a yellow color, whereas when the mix i a glass to secure by Letters Patent is:

1. A glass having'a low silica content, a high alumina content, the qualities of transparency and high electrical insulation under heat, and containing an alkaline earth oxid.

2. A glass havin a high alumina content, a low co-eflicient 0 expansion, substantially no alkali content, containing an kaline earth oxid and having the quality of transparency.

3. A glass containing calcium oxid, having a low silica content, a hi h alumina content, substantially no alka i content, and

having the qualities of trans arency and of high electrical insulation un er heat.

4. A glass containing boric oxid, having a low silica content, a high alumina content, substantially no alkali content, and-the quality of transparency. a

' 5. A glass containing calcium oxld and boric oxid and having a low silica content, a high alumina content and substantially no alkali content. 4

6. A glass having a low silica content, a high alumina content, substantially no alkali content, and showing by analysis the presence of fluorine.

7. A glass low in silica, high in alumina, having the quality of transparency and showing by analysis the presence of fluorine.

8. A glass containing between 25% and 55% of silica, boric oxid, calcium oxid, and at least 10% of alumina, and having the qualities of'trans arency and high electrical insulation under heat.

9. A glass containing silica, boric oxid, at least 10% of alumina and calcium oxid, being substantially free from alkali and having a co-efiicient of expansion not greater than .0000050. i

10. A glas containin .and having a co-eflicient of expansion not .alysis the presence of fluorine an lit-least 20% of alumina, at least 25% o silica, boric oxid,

greater than .0000050, and the quality of high electrical insulation under heat.

12. A glass containing at least 20% alumina, at least 25% of silica, an alkaline earth oxid and having the qualities of transparency and high electrical insulation under heat. v 1

v 13. A glass containing silica, boric oxid, a hi h content of alumina, an alkaline earth oxid, lead oxid being substantially free from alkali and having the qualities of low expansion and high stability.

14. A glass containing silica, boric oxid,

lead oxid, an alkaline earthoxid, and alumina, having a low co-efiicient of expansion and the qualities oftransparency and high electrical insulation under heat.

15. A glass containing 40% to of silica not less'than 15% of alumina, not less than 10% of boric oxid, calcium oxid and being substantially free from alkali.

16..A glass containing at least 40% of silica, at least 15% of alumina and calcium oxid and being substantially free from alkali and having the quality of transparency.

17. A glass containing no alkali, having a large content of alumlna showin by anthe quality of transparency.

18. A glass containing between 25% and 57% of silica, at least 20% of alumina, be-

tween 9% and27% of boric oxid, between 5% and 20% of calcium oxid, and having the qualities of transparency and high electrical insulation under heat.

19. A glass containing 25% to 57% of silica, boric oxid 9% to 27%, alumina'12% to 23% and alkaline earth metal oxid, said glass having the quality of transparency and high electrical insulation under heat.

20. A glass batch containing silica, alumina, and calcium fluoride, and capable of forming a clear transparent glass having a linear co-eificient of expansion of less than .0000050, and the quality of high electricalinsulation, under heat.

21.'A glass batch containing silica, at least 15% of alumina, calcium fluoride, boric acid, and capable of making a transparent glass having the quality of high electrical insulation under heat.

having v 22 A glass batch containing silica, allimina, calcium fluoride, boric acid, and lead oxid, and capable of'making a transparent glass having the quality of high electrical insulation under heat" and having a coeflicient of expansion of less than .0000050.

- FRED M. LOCKE. FRED J. LOCKE. 

